1. Field of the Invention
The present invention relates to an alignment mark used in the manufacture of a semiconductor device, and to an aligning method using the alignment mark.
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2001-115256, filed Apr. 13, 2001, which is herein incorporated by reference in its entirely for all purposes.
2. Description of the Related Art
An exposure apparatus transfers circuit patterns of a plurality of masks to the surface of a semiconductor substrate. Prior to the exposure process, the exposure apparatus identifies an alignment mark formed on the semiconductor substrate and aligns the mask with reference to the alignment mark.
A conventional alignment mark is defined within a rectangular region and includes a plurality of alignment patterns. The alignment patterns are, for example, plural sets of parallel slits where each set consist of three regularly spaced slits. A laser light is diffracted and scattered by the slits and then detected to identify the alignment mark. And, manufacturing process steps of such the slits having a bump are described below.
In the manufacture of the alignment mark, after a coated layer is formed on the semiconductor substrate, the circuit patterns are transferred to the coated layer by a lithography etching process. At the same time, the alignment mark is formed. Then, another coated layer is formed on the semiconductor substrate having the alignment mark formed thereon, and a photo resist is formed on this other coated layer.
At the exposure apparatus, the alignment mark is irradiated by the laser light, and a movement of the laser light is detected in response to a movement of a stage of the exposure apparatus which positions the semiconductor substrate. Then, a reflected light is diffracted and scattered at the three slits of the alignment mark. The reflected light returns through the same light path and then separates. The separated reflected light is detected by a detector of the exposure apparatus. A position of the alignment mark is recognized from a diffracted light which enters into the detector.
The exposure apparatus corrects an exposure position in accordance with a difference between the recognized position of the alignment mark and an origin of the mask.
However, in the conventional alignment mark, a space between the closest slit of the alignment mark to a side of the rectangular region of the alignment mark and the side may be equal to a space between the three regularly spaced slits. In such cases, the exposure apparatus may incorrectly recognize the diffracting and scattering of light arise from the side of the rectangular region of the alignment mark, as a substitute for the diffracting and scattering of light arising from the 3 regularly spaced slits of the alignment mark.